The present disclosure relates to permanent magnet machines. More particularly, the present disclosure relates to a high-speed permanent magnet machine with high power density.
Interior Permanent Magnet Machines (IPMs) such as permanent magnet motors and generators have been widely used in a variety of applications including aircraft, automobile, subsea and industrial usage. A requirement for lightweight and high power density permanent magnet machines has resulted in the design of higher speed motors and generators to maximize the power to weight ratios. Hence, the trend is increasing acceptance of permanent magnet machines offering high machine speed, high power density, reduced mass and cost.
Permanent magnet machines typically employ permanent magnets either in the rotor, the stator or both. In most instances, the permanent magnets are found within the rotor assembly. The output power of the permanent magnet machine is determined by the length, diameter, air gap magnetic flux, armature current density, speed, and cooling ability of the stator and rotor assemblies.
In conventional internal permanent magnet machines, multiple permanent magnets are embedded inside multiple laminations of a rotor. The mechanical stresses in the rotor are concentrated in multiple bridges and center posts. For higher speed applications, the thickness of the multiple bridges and center posts have to be increased for enhanced structural strength of the rotor and various other parts. The bridges of posts with increased thickness lead to higher magnet flux leakage, which significantly reduces the machine power density, resulting in decreased efficiency of the machine.
In one specific embodiment, segmented permanent magnets are captured by a sleeve component, and more particularly an Inconel sleeve configured about the permanent magnets. The Inconel sleeve encompasses the magnets and provides support for the magnets in the radial direction. The maximum rotational speed of the rotor is dependent on the thickness of the Inconel sleeve and the mass of the permanent magnets. The speed at which the rotor can turn safely is limited by centrifugal loading on the permanent magnets and the overall weight, including that of the sleeve component. In addition, for radial machines and general armature types, the sleeve component needs to be non-magnetic to avoid shorting the flux path before it moves from rotor to armature. It would transport flux better if it were magnetic, but that would require some kind of non-magnetic separations in the shell between the locations of the magnetic poles, and this would be a difficult-to-construct composite material. In other words, the magnetic circuit, or total magnetic reluctance, needs to be optimal.
Therefore, it is desirable to provide a permanent magnet machine including a sleeve component having an increased centrifugal load capacity in light of reduced overall weight, so as to provide increased power density and improved electrical performance.